Women who smoke face an increased risk of breast cancer, according to a study, and a higher risk still if they smoke before having their first child.
Researchers with the American Cancer Society analyzed data from 73,388 women in the Cancer Prevention Study II Nutrition Cohort. Analyses were based on 3,721 invasive breast cancer case patients identified during a median follow-up of 13.8 years, according to the study abstract.
Among the study cohort, incidence was 24% higher in current smokers and 13% higher in former smokers than in those who never smoked, the researchers calculated. Women who initiated smoking before menarche had a 61% higher risk, and those who began smoking after menarche but 11 or more years before their first birth had a 45% higher risk. No relationships were observed with other smoking parameters.
Alcohol consumption did not confound associations with smoking status, although among those who never drank, neither current nor former smoking was associated with an increased risk of breast cancer.
The researchers also conducted a meta-analysis of 14 previous cohort studies. In that data, they found, current and former smoking were “weakly associated with risk.” They found a stronger association — a 21% increase — among women who initiated smoking before first birth.
“These results support the hypothesis that active smoking is associated with increased breast cancer risk for women who initiate smoking before first birth and suggest that smoking might play a role in breast cancer initiation,” the authors wrote.
The study is scheduled for publication in the Journal of the National Cancer Institute and is available via subscription or purchase at http://jnci.oxfordjournals.org/content/early/2013/02/26/jnci.djt023.full.